The present invention relates to fluid flow control devices. More particularly, this invention is directed to valves having resilient deformable seats.
It has long been recognized in valve construction that interposing a resilient deformable member between the valve seat and movable valve member results in an efficient seal. The reasons for this are many. First, the cooperating components, which are customarily metal members, can not be so precisely formed as to provide perfectly matched seating surfaces. A deformable member has the capability of accommodating irregularities in the seating surfaces. Second, corrosion and flow induced wear create surface imperfections in the seating surfaces. Resilient members compensate for this deterioration, extending the service life of the valve. Also, foreign particles may adhere to the seating surfaces. Such particles serve to hold or prop, i.e., crack, open the valve. The deformable members can often absorb the foreign particles allowing leak proof closure. Finally, resilient deformable valve seats are designed to be replaceable components thereby facilitating valve repair when necessary.
The conventional valve designs which utilize a resilient seat member rely upon a single line of contact between the seat and movable valve member, i.e. the plug, to establish a seal when the valve is in the closed state. Although compression of the resilient seat member may widen the contact line, the area of contact may nevertheless be insufficient to bridge large surface crevices or absorb large foreign particles. Additionally, operating conditions such as high compression, extremes in operating temperature or exposure to certain fluid mediums may cause the resilient member to adhere to the valve member and resist separation therefrom. Ultimate separation, i.e., sliding out of the valve seat and/or plug, can cause scratches in the resiliant member which can lead to failure.
A previous approach to overcoming the above-discussed operating problems employed a "floating" seat member and is shown in U.S. Pat. No. 3,598,145. While the use of a floating seat comprised of a material having a low coefficient of friction has provided an exceptionally reliable valve, failures have nevertheless occured under unusual and exceptionally harsh operating conditions. This was particularly true in high pressure applications with dirty fluids.
Another prior art approach to enhancing valve integrity is depicted in U.S. Pat. No. 3,809,362. The seats of valves of the type as depicted in U.S. Pat. No. 3,809,362 have typically had a region where the seat was subjected to bending about an edge on a supporting metal member. The stresses in this bending region have led to premature failure, particularly when the valve was subjected to extremes in temperature.